package abe;

import java.util.Iterator;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

/**
 * This class allows line-by-line iteration through a text file.
 * The iterator's remove() method throws UnsupportedOperatorException.
 * The iterator wraps and rethrows IOExceptions as IllegalArgumentExceptions.
 */
public class TextFile implements Iterable<String> {

  // Used by the TextFileIterator class below
  final String filename;

  public TextFile(String filename) { 
    this.filename = filename; 
  }

  // This is the one method of the Iterable interface
  public Iterator<String> iterator() { 
    return new TextFileIterator(); 
  }


  // This non-static member class is the iterator implementation
  class TextFileIterator implements Iterator<String> {

    // The stream we're reading from
    BufferedReader in;

    // Return value of next call to next()
    String nextline;

    public TextFileIterator() {
      // Open the file and read and remember the first line.
      // We peek ahead like this for the benefit of hasNext().
      try {
        in = new BufferedReader(new FileReader(filename));
        nextline = in.readLine();
      } catch(IOException e) { 
        throw new IllegalArgumentException(e); 
      }
    }

    // If the next line is non-null, then we have a next line
    public boolean hasNext() { 
      return nextline != null; 
    }

    // Return the next line, but first read the line that follows it.
    public String next() {
      try {
        String result = nextline;

        // If we haven't reached EOF yet
        if (nextline != null) {  
          nextline = in.readLine(); // Read another line
          if (nextline == null) 
            in.close();             // And close on EOF
        }

        // Return the line we read last time through.
        return result;
      } catch(IOException e) { 
        throw new IllegalArgumentException(e); 
      }
    }

    // The file is read-only; we don't allow lines to be removed.
    public void remove() { 
      throw new UnsupportedOperationException(); 
    }
  }

  public static void main(String[] args) {
    String filename = "service.log";
    if (args.length > 0) 
      filename = args[0];

    for(String line : new TextFile(filename))
      System.out.println(line);
  }
}